Inhibition of corrosion in return steam condensate lines



United States INHIBITION OF CORROSION IN RETURN STEAM CONDENSATE LDIES John W. Ryznar, La Grange Park, 111., and Willard H. Kirkpatrick, Sugar Land, Tern, assignors to National Aluminate Corporation, Chicago, Ill., a corporation of Delaware No Drawing. Application April 36, 1952, Serial No. 285,322

7 Claims. (Cl. 210-23) This invention relates to a new and improved method for inhibiting corrosion in return steam condensate lines.

It is well known that steam lines and steam condensate lines are subject to corrosion which is very difficult to control. This corrosion is apparently due, to a large extent, to carbonic acid formed by carbon dioxide contacting the liquid phase in. a boiler-steam-condensate systern.

Steam vapor leaves the boiler uniformly mixed with any carbon dioxide present. Non-uniform distribution of the carbon dioxide begins to exist the instant that liquid droplets are formed in the steam because the carbon dioxide dissolves in the liquid. While the rate of con densation from the vapor depends on heat transfer and pressure changes the rate of dissolving of the carbon dioxide in the condensate depends on such factors as temperature, pressure, alkalinity, contact time, etc., and these conditions are different in the various parts of any steam-condensate system. Higher condensing rates of steam are known to increase the carbon dioxide content of the condensate, assuming equal carbon dioxide concentrations in the incoming steam. In the varied uses of steam as in radiators, heat exchangers and evaporators, different condensing rates are encountered and different carbonic acid concentrations are obtained. The design of the apparatus and the steam and condensate temperatures will also have some influence on the carbonic acid concentrations encountered. Carry-over from the boiler water can also increase the corrosion.

It is known to use a readily volatile alkaline amine material for protection against corrosion in steam and re turn condensate lines but the results obtained with such amines have left much to be desired, particularly in steam and condensate systems of great length or in tall buildings.

The addition of a relatively non-volatile amine to a steam condensate system is not a new idea but in actual practice the employment of such amines has been hampered by insufficient knowledge of the best amine to use, and by inadequate corrosion prevention with many types of such amines.

One of the objects of the present invention isto provide a new and improved method of inhibiting corrosion in return steam condensate lines.

Another object of the invention is to provide a com position for the treatment of steam condensates which produces improved results in preventing or minimizing corrosion in steam lines, traps and condensers. Other objects will appear hereinafter.

In accomplishing these objects in accordance with this invention it has been found that new and improved results can be obtained by treating the steam condensate or the metal surfaces on which the steam condenses with a quantity of a condensation product derived from the reaction of an aliphatic polyamine containing primary and/ or secondary amino groups, preferably a polyethylene polyamine or a polypropylene polyamine, and

an organic carboxy acid containing at least eight carbon atoms, preferably a mixture of two dissimilar monocarboxy acids, one being an unsaturated long chain organic acyclic monocarboxy acid containing at least eight carbon atoms and the other being an unsaturated organic carbocyclic acidic resin-type monocarboxy acid, for instance, abietic acid. The reaction is effected at temperatures sufiiciently high to cause formation of an amide and under conditions facilitating the elimination of an aqueous distillate. In general, the temperature should be at least C. and preferably within the range of 115 C. to 300 C. The heating is continued at progressively higher temperatures until a major proportion of the chemically available water is removed. The amidification (or N-acylation) reaction takes place primarily between the primary amino groups of the polyamine and the carboxylic acid groups of the carboxy acid, it being understood, however, that the amidification reaction can also occur between any secondary amino groups present in the polyamine and a carboxy group of the carboxy acid.

Where two dissimilar carboxy acids are employed in preparing the polyamides, the one is preferably an unsaturated long chain acyclic or fatty-type carboxy acid having at least eight carbon atoms and not more than thirty-six carbon atoms in the chain. This group of acids can also be called unsaturated detergent-forming acids. As examples of acyclic-type acids which have been found to be particularly suitable for the purpose of the invention there may be mentioned linolenic acid, linoleic acid, oleic acid, mixtures thereof and other commonly available unsaturated long chain acyclic acids. Of these acids those having a plurality of double bonds (e. g., linoleic acid and linolenic acid) can also be called drying oil acids. Especially good results have been obtained in the practice of the invention by using compositions which are derived in part from mixtures of drying oil and non-drying (e. g., oleic acid) oil fatty acids.

The most commonly available carbocyclic organic carboxy acids suitable for the preparation of polyamides for the practice of the invention are abietic acid and related derivatives derived from naval stores. Other acidic resins, e. g., polymerized rosin, dehydrogenated rosin and cracked copals (for example, run Congo) may be employed. These rosin acids may be characterized as oil soluble acidic resins having an acid value of at least 30. In most cases, the acid value will be above 50, and in the case of rosin it exceeds 150.

The mixed polyamides derived from an aliphatic polyamine of the type described and mixtures of unsaturated acyclic and carbocyclic carboxy acids have been more effective in preventing the corrosion of ferrous metals under conditions existing in steam condensate systems than the individual polyamides.

In the preferred practice of the invention the weight ratio of the acyclic carboxy acid to the carbocyclic-carboxy acid in the composition is preferably within the range of 1:2 to 5:1, the lesser component always being in excess of about 15% of the total carboxy acids.

While any blend of the dissimilar acids can be prepared, our preferred mixture of dissimilar carboxy acids is readily obtainable as a naturally occurring mixture of dissimilar carboxy acids known in the trade as tall oil. Tall oil is the liquid resin obtained in digesting wood to wood pulp in the paper industry. It is a dark brown, viscous liquid containing a crystalline sediment of abietic acid. From the results of several investigators the following principal constituents of tall oil are indicated: resin acids 30 to 45%, fatty acids 45 to 60%, unsaponifiable matter 6 to 12%. The unsaponifiable portion is a yellow viscous oil containing a waxy or pitchy material,

The specifications of the particular grade of tall oil which we prefer to use is as follows:

Specific gravity (at 155 C.) .9697 Acid number 164.0 Saponification number 173.6 Ester number 9.4 Percent moisture 0.0 Percent rosin 39.2 Percent fatty acids (by difierence) 52.79

Percent linolenic acid 19.25

Percent linoleic acid 10.5

Percent oleic acid 23.04 Percent unsaponifiable 8.01 Ilodine number 148.83 Thiocyanogen-iodine number 91.1 Percent saturated fatty acids None Percent unsaturated fatty acids 100 Titer test 5.5 C. Pour test 4.4 C. Cloud test l2.8 C.

The condensation products employed for the purpose of the invention are all substantially insoluble in water and relatively non-volatile with steam. They are preferably derived from unsaturated organic carboxy acids, but suitable condensation products can also be prepared from saturated organic carboxy acids, such as, for ex ample, lauric acid, myristic acid, palmitic acid, stearic acid and higher homologues. In general, the amides derived from the unsaturated organic carboxy acids are more readily dispersible in water than those derived from the saturated organic carboxy acids but this will vary depending upon whether the condensation product contains an excess of the organic carboxy acid or an excess of the polyamine as hereafter described.

The polyamines employed in making condensation products for use in accordance with the invention are aliphatic polyamines containing at least two amino groups capable of amidification, i. e., at least two primary amino groups, or at least one primary amino group and one secondary amino group, or at least two secondary amino groups. If the amine contains two terminal primary amino groups and a connecting alkylene chain as in ethylene diamine or decamethylene diamine it is referred to herein as an alkylene diamine. If the amine contains two terminal primary amino groups and one or more secondary amino groups interconnected by alkylene chains the amine is referred to herein as a polyalkylene poly-amine. If the amine contains two terminal primary amino groups and a connecting allrylene chain interrupted by one or more ether linkages as in beta, betadiaminodiethyl ether and higher ethylene, propylene and other homologues, it is referred to herein as an oxyalkylene diamine. If one or more of the alkylene groups in the alkylene diamine contains a hydroxyl group as in 1,3-diamino-2-propanol it is referred to herein as a hydroxy alkylene diamine. If one or more of the nitrogen atom-s in the alkylene diamine has attached thereto a hydroxyalkyl radical as in hydroxyethylethylene diaminc (aminoe'thylethanol amine) it is referred to herein as a hydroxyalkyl alkylene diamine. If one or more of the alkylene groups in the polyalkylene polyamines contains a hydroxyl group it is referred to herein as a hydroxy polyalkylene polyamine. If one or more of the nitrogen atoms in the polyalkylene polyamines has attached thereto ahydnoxyalkyl radical it is referred to herein as a hydroxyalkyl polyalkylene polyamine. The preferred amines are the polyalkylene polyamines and the hydroxy polyalkylene polyamines in which the alkylene groups contain either two or three carbon atoms.

As examples of specific polyamines which can be employed to prepare condensation products suitable for the practice of the invention there may be mentioned ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentam-ine, di'-( 1,2-propylene) triamine, hy

4 droxyethylethylenediamine, hydroxyethyldiethylenetriamine and complex still residues remaining from the production of alkylene amines and alkylolamines.

One such complex still residue is polyamine H which is a still residue remaining from the production of ethylene amines. In the manufacture of ethylene amines ethylene dichloride is reacted with ammonia. The reaction conditions vary but in all cases a mixture of the members of the series is obtained. At comparatively low temperatures and pressures predominantly ethylenediamine is formed together with some polyethylene polyamines. At higher temperatures and pressures the proportion of the polyethylene polyamines is higher. In the recovery of the higher molecular weight polyethylene polyamines by distillation there remains a still residue which constitutes the polyamine H and consists of homologues higher than tetraethylenepentamine. Similar still residues from the production of other polyalkylene polyamines such as polypropylene polyamines are suitable for use in preparing condensation products employed for the purpose of the invention.

The condensation reaction with the elimination of an aqueous distillate can be carried out by mixing the organic carboxy acid and the polyamine and heating the reaction mixture under conditions facilitating the elimination of an aqueous distillate but stopping the reaction short of gel formation. The end product should be water wettable to some extent.

The reaction can also be effected in the presence of a suitable solvent which is adaptable to azeotropic distillation. A suitable solvent for this purpose is sulfur dioxide extract which is a by-product from the Edeleanu process of refining petroleum in which the undesirable fractions are removed by extraction With liquid sulfur dioxide. After removal of the sulfur dioxide a mixture of hydrocarbons, substantially aromatic in character, remains which is designated in the trade as S02 extract. Examples of other suitable hydrocarbon vehicles are Gray Tower polymers, toluene, xylene, gas oil, diesel fuel, bunker fuel and coal tar solvents. The above cited examples of solvents are adaptable to azeotropic distillation as would also be any other solvent which is immiscible with water, miscible with the reacting mass and has a boiling point or boiling range in excess of the boiling point of water.

The proportions of the organic carboxy acid and the polyamine are calculated to completely acylate at least one mol of nitrogen in the polyamine and in the preferred products the proportions of the carboxy acid are sufiicient to acylate at least two and preferably three mo ls :of nitrogen in the polyamiue. The quantity of the polyamine employed is such that the molar ratio of nitrogen in the amino groups to carboxy in the organic carboxy acid is within the range of 4:1 to 1:2. Where the condensation product contains an ,excess of free amine which has not been acylated such products can be dissolved without difiiculty in the. steam condensate. Where the condensation products contain an excess of the organic car-boxy acid which is not reacted with the polyamine they can be dissolved in a solution of ethyl alcohol and added as an alcoholic solution to the steam condensate or an additional quantity of the polyamine can be added to such products in orderto increase their solubility. For example, about 2% to 5% of a polyamine such as diethylenetriamine or triethylenetet-ramine or other liquid polyamines can be employed for this purpose. instead of an alcohol another water miscible solvent can be used such as ethylene glycol, diethylene glycol, the moncbutyl ether of diethylene glycol and similar solvents of this type.

In order to evaluate the invention a series of corrosion tests were made in an experimental steam condensate system. In this system a synthetic condensate was produced in a glass tower by aerating heated distilled Water with a mixture of carbon dioxide andair. This condensate and a solution of the treating chemical were proportioned into a test container by gravity feed. A number of steel test coupons were suspended in the latter and the liquid was mildly agitated with a paddle stirrer. At periodic intervals a test specimen was removed from the bath and the weight loss determined. The temperature, free carbon dioxide and dissolved oxygen of the synthetic condensate, and the treatment concentration were controlled throughout the test.

In the synthetic condensate system three five-gallon bottles were supported above the test jar for replacement of the solution in the bath. A condensate equilibrium tower constructed from a 48 inch Pyrex tube 2% inches diameter was mounted above the bath. Distilled water or its equivalent was discharged from the S-gallon reservoirs into the middle of the tower through a rubber stopper in the base of the tube. The water was heated with a 500 watt heater which was constructed by wrapping the lower half of the tower with Nichrome resistance ribbon. The temperature of the water was thermostatically controlled at 150i5 F. with a thermoreg ulator which extended through the stopper in the bottom of the tube. A disc-type dispersion tube was also placed in this stopper so that the water could be aerated with a 5.4:1 mixture of air and carbon dioxide at the rate of 130 cc. per minute. The gas passing through the liquid in the tower was discharged to the test container through a stopper inserted in the top of the tower.

The corrosion inhibiting chemical was metered into the bath from a Pyrex tube mounted above the test container and connected to the system between the outlet of the tower and the inlet to the test container. Depending on the solvent used to dissolve the treating chemical the height of the feed tube above the bath was adjusted to compensate for the diiference in the densities of the solvent and the distilled water. A soda-lime tube was placed in the top of the tube containing the treating chemical to prevent evaporation and the absorption of carbon dioxide from the atmosphere.

The air and carbon dioxide were controlled by reducing the line pressure with diaphragm valves and controlling the fiow with a differential flow regulator. The flow rates were measured with manometer-type flow meters. The air and carbon dioxide were metered into a mixing chamber which was filled with inch Berl saddles. This gas mixture was then discharged into a distributor from which it was metered in an aerator into a tower or test bath.

The corrosion test specimens consisted of 1 inch x 2 inch panels which were sheared from a single sheet of 20-gauge cold rolled mild steel. All specimens were uniformly abraded with No. 2 emery paper, polished with No. 1 emery paper and rinsed with acetone and toluene before being immersed in the bath.

The test bath was filled with 4% gallons of distilled water or its equivalent. Agitation of the liquid was initiated and the water in the bath was heated to and thermostatically controlled at 150:1" F. The free carbon dioxide and dissolved oxygen of the water were maintained at 45 :4 parts per million and 3.5i0.2 parts per million, respectively, by aerating with a 5.4:1 mixture of air and carbon dioxide at the rate of 90 cc. per minute.

After equilibrating the bath in this manner for 24 hours aeration of the bath was discontinued and initiated in the condensate equilibrium tower. When the water in the tower was heated to l50- 5 F., the regulated temperature, the effluent tube on the bath was lowered so that the liquid would be discharged from the bath at 26 ml. per minute or gallons per 24 hours. As soon as the system reached equilibrium the desired amount of treating chemical was added to the bath and treatment tube. The system was conditioned in this manner for 24 hours to eliminate the possibility of depletion of the 6 inhibitor in the solution due to adsorption on the surface of the bath.

Six of the test coupons were then weighed on an analytical balance to the closest 0.1 mg. and placed in the test containers. A specimen was removed from the bath periodically and was cleaned by 30-second immersions in inhibited muriatic acid followed by neutralization in a saturated sodium carbonate solution. When all of the corrosion products had been removed from the coupon it was rinsed with distilled water, dried by dipping in acetone and reweighed.

Samples of the water in the bath were collected each day and the free carbon dioxide of the bath liquid was determined at least once each day.

The following examples illustrate the results obtained in the evaluation of test specimens using treating chemicals within the scope of the invention.

Example I A solution of diabietyldiethylenetriamine in denatured ethyl alcohol was added to the steam condensate system in the test procedure previously described in a concentration of 10 parts of the diabietyldiethylenetriamine per million parts of condensate. A blank test of the condensate to which no inhibiting chemical had been added showed a weight loss in the test specimens after 1, 2, 3, 4, 5 and 6 days of 33.2, 65.7, 89.3, 133, 226 and 263 mg., respectively. After the addition of 10 parts per million (p. p. m.) of the diabietyldiethylenetriamine to the test condensate the weight loss of the specimens during the same period of time was 3.5, 7.4, 10.8, 15.3, 17.2 and 25.4 mg, respectively.

Example 11 The test procedure was the same as that previously described. In a condensate to which no inhibiting chemical had been added the weight lost by the specimens after 1, 2, 3, 4, 5 and 6 days was 33.7, 70.1, 150, 223, 271 and 394 mg, respectively. In the same condensate after the addition of 10 p. p. m. of dioleyl diethylenetriamine in a solution of denatured ethyl alcohol, the weight loss of the test specimens was 7.2, 12.1, 15.9, 15.4, 18.5 and 18 mg. after the first, second, third, fourth, fifth and sixth days, respectively.

Example III The test procedure was the same as that previously described. The results in the blank test were the same as those described in Example II. The treating chemical was prepared by reacting together 45.75% by weight of oleic acid, 45.75 by weight of tall oil and 8.5% by weight of diethylenetriamine in a kettle heated to a temperature of about C. to 116 C. with steam at 25 pounds per square inch pressure (gauge) for a period of 24 hours and venting the aqueous distillate to the atmosphere. 50 p. p. m. of this product in a denatured ethyl alcohol solution when added to the condensate in the test system previously described inhibited corrosion of the test specimens to the extent that the weight loss in mg. was 2.4, 4.8, 5.0, 5.4, 2.3 and 4.8 after the first to sixth days, respectively.

Example IV The procedure was the same as that described in Example Ill except that the amount of the inhibiting chemical added to the condensate system was only 10 p. p. m. The Weight lost by the specimens in mg. after 1, 2, 3, 4, Sand 6 days was 1.8, 2.1, 1.8, 1.9, 2.1 and 1.8 mg, respectively.

Example V The test procedure was the same a that previously described. The corrosion inhibiting chemical was prepared as follows:

Six hundred (600) parts of crude tall oil and 206 parts of diethylenetriamine were heated in a reaction flask provided with means of stirring and for removal of any aqueous distillate that may form during the course of the reaction. The amine and tall oil were heated and at 160 C. an aqueous distillate began to form. Heating was continued until a total of 36 parts of aqueous distillate has been secured. This was obtained in approximately 1 /2 hours at a maximum temperature of 200 C. TWo hundred (200) parts of this amide intermediate was mixed with 100 parts of 99% isopropanol.

Ten parts of this composition per million parts of steam condensate when tested in the manner previously described resulted in a weight lost by the test specimens of 2.0, 3.1, 4.4, 4.6, 7.4 and 7.1 mg. after the first, second, third, fourth, fifth and sixth days, respectively. In this test the test chemical was added to the condensate system in a solution of denatured ethyl alcohol.

The blank test results were the same as those described in Example I.

Example VI The procedure and the test chemical were the same as those described in Example V except that the test chemical was added in an aqueous solution in a concentration of 50 parts per million parts by weight of the condensate and the weight lost by the test specimens was 2.6, 3.6, 3.2, 2.7, 2.5 and 3.3 mg. after the first, second, third, fourth, fifth and sixth days, respectively.

Example VII The test chemical was prepared by heating 600 parts of crude tall oil with 292 parts of triethylene tetramine in similar equipment to that described in Example V. At 156 C. an aqueous distillate began to form and heating was continued with agitation until a total of 36 parts of aqueous distillate had been secured. This required approximately 1 hour at a maximum temperature of 225 C. To 200 parts of this amide intermediate there was added 225 parts of 99% isopropanol.

When this product in a denatured ethyl alcohol solution was added to a condensate in proportions of p. p. In. by weight of the condensate and tested according to the test procedure previously described, the weight lost by the test specimens was 4.2, 5.8, 6.9, 7.1, 9.0 and 10.7 mg. after the first, second, third, fourth, fifth and sixth days, respectively.

Example VIII When the test chemical described in Example VII in the form of an aqueous solution was added to a condensate in proportions of 50 p. p. m. by weight of the condensate and tested in the manner previously described, the weight lost by the test specimens was 3.4, 2.2, 1.6, 1.9, 2.3 and 2.7 mg. after the first, second, third, fourth, fifth and sixth days, respectively.

The blank test results in Examples VII and VIII were the same as those described in Example I.

Example IX The test chemical was prepared by heating 600 parts of crude tall oil with 300 parts of polyamine H, which is a still residue product from the manufacture of polyalkylene polyamine. The tall oil and polyamine H were heated and at 148 C. an aqueous distillate began to appear. Heating was continued for approximately 2 hours additional time to secure a total of 36 parts of aqueous distillate at a maximum temperature of 225 C. Two hundred (200) parts of this amide was then mixed with 50 parts of 99% isopropanol and 50 parts of water.

When this product in an aqueous solution was added to a condensate in a test system previously described in proportions of 50 p. p. m. by weight of the condensate, the weight lost by the test specimens was 1.9, 2.5, 2.3, 2.0, 4.1 and 2.9 mg. after the first, second, third, fourth, fifth and sixth days, respectively.

The blank test results were the-same as those-described in Example I.

Example X When the test chemical described in Example IX in 'a' denatured ethyl alcoholsolution was added toa condensate in a test system of the type previously describeda'nd in proportions of 10 p. p. m. by weight of the condensate, the weight lost by the test specimens was 2.2, 2.2, "5.0; 5.4, 7.0 and 16.9 mg. after the first, second, third, fourth, fifth and sixth days, respectively.

The blank test results were the same as those described in' Example II.

It will be observed that in the products tested in Exampies .l and II the amide was the reaction product of two mols of an organic carboxy acidand one moi-of diethylenetriamine. In Examples III and IV there is an excess of the organic carboxy acid' over that theoretically required to form the diamide. In Examples VI to X there is an excess of the polyamine in'terms of. the relative ratio of nitrogen atoms in the amino groups to carboxy groups in the organic-carboxy acid.

In order to compare the results obtained with amides outside of the scope of the present invention the monocaproamide of ethylenediamine in a denatured ethyl alcohol solution was tested according tothe test procedure previously described by adding it in proportions of 50 p. p. m. by weight of a condensate corresponding to that used in Example II and the weight lost by the test specimens was 77.9, 152, 252, 339, 418 and 532 mg. after 1, 2, 3, 4, Sand 6 days, respectively. Thus, it was shown that this material had no corrosion inhibiting effect, in fact the weight lost by the test specimens 'was greater than that lost without the addition of any chemical and hence there was an acceleration of corrosion.

Example XI The test chemical was prepared in the form of an emulsion. This emulsion was prepared by adding diethylenetriamine to the reaction product of 45.75% oleic acid,

45.75% tall oil and 8.5% diethylenetriamine and emulsifying with water. The resultantemulsion contained 20% by weight of the active corrosion inhibiting reaction product, 2.75% by weight of diethylenetriamine and 77:25% by weight of water.

The test procedure was the same as that previously described except that' it was carried on for a period 0530 days. The quantity of the test chemical was 50 p. p. m. of the emulsion by weight of the condensate which is equivalent to 10 p. p. m. by weight of the condensate of the active corrosion inhibiting chemical. The test specimens were weighed every fifth day. The weight loss in mg. was as follows:

In a comparable test with octadecylamine acetate in proportions of 10 p. p. m. by weight of the condensate the weight loss was as follows:

Days exposed: Weight loss, mg.

Octadecylamine acetate is a material of a difierent type from that employed in the practice of the. present inventron which has heretofore been recommended for the Days exposed: Weight loss, mg.

It will be observed that the morpholine was much less effective than the active corrosion inhibiting chemicals employed in accordance with the present invention despite the fact that morpholine has been used for many years as an addition agent to boiler waters to prevent corrosion in steam condensate lines by volatilization of the morpholine from the boiler water.

It will be understood that some variations can be made in the preparation of the corrosion inhibiting chemicals and in the procedures employed in using such chemicals. Although the preferred inhibiting compositions are prepared by reacting organic monocarboxy acids, preferably unsaturated monocarboxy acyclic and carbocyclic acids, with polyamines, it is also possible .to employ organic polycarboxy acids such as dilinoleic acid, commonly known as dimer acid, and the acids known in the trade as VR fatty acid and VR-l acid. VR fatty acid is an organic carboxy acid material which is a vegetable residue resulting from the distillation of soap stock. This material contains ester bodies and has the following characteristics:

Acid value 45 Saponification value 150 Iodine value 100 Color (Bartlett) 13 Viscosity (Zahn G5 at 75 C.) seconds 15 Acid number 150 Iodine number 36 Saponification number 172 Unsaponifiable matter "percent" 3.7, 3.5 Moisture content do 0.86

Certain of the compositions employed herein as corrosion inhibiting agents in steam condensate systems have been used heretofore as antifoam agents in steam generation but under the conditions of such use these compositions were not effective in inhibiting corrosion in steam condensate return lines. In the first place, when such compositions have been employed heretofore as antifoam agents they have been added to the feed waters to the boiler in very small amounts. These amounts are usually within the range of 0.001 to 0.1 grain per gallon or not more than 1.7 parts per million by weight of the feed water. Secondly, these compositions are hydrophobic and relatively non-volatile with steam, and in the small amounts which they were present in the boiler water enough of the composition would not be volatilized to produce a substantial corrosion inhibiting effect in the steam condensate system. Accordingly, no such effect was heretofore observed with these compositions when they were added to boiler water as antifoa'rn agents. In order to be effective, inhibiting compositions should be added to the steam condensate return system so that they can form a coating or film on the metal surfaces. In general, it is preferred to add the corrosion inhibiting material to the steam condensate line. The proportions preferably should be at least five parts per million of the corrosion inhibiting chemical by weight of the steam condensate and the best results have been obtained with quantities within the range of 10 to 50 parts per million of the corrosion inhibiting chemical by weight of the steam condensate.

The employment of the corrosion inhibiting chemicals in accordance with this invention is applicable to the generation of steam at various temperatures and pressures. Good results can be obtained where steam is generated under atmospheric conditions, subatmospheric conditions or superatmospheric conditions. In most cases, steam is generated at pressures from atmospheric up to 1500 pounds pounds per square inch and the corresponding temperatures.

The chemical inhibiting compositions employed in accordance with the present invention are film-forming or barrier-type inhibitors. They are unusually effective in preventing corrosion of the internal surfaces of steam condensate return lines. Heretofore many difficulties have been experienced due to pitting, grooving and ultimate deterioration of sections of steam condensate return systems and the plugging or constrictions in the system with the insoluble products of corrosion. The chemical treatment of steam condensate return systems as described herein makes it possible to control and inhibit corrosion in such systems.

The invention is hereby claimed as follows:

1. A method of inhibiting corrosion in return steam condensate lines which comprises introducing into the return steam condensate system a quantity of a composition resulting from heating an organic carboxy acid containing at least 8 carbon atoms and an aliphatic polyamine containing at least two amino groups from the group consisting of primary and secondary amino groups, at a temperature of at least 115 C. and the elimination of an aqueous distillate, the proportions of said carboxy acid being suflicient to acylate at least one mol of nitrogen in said polyamine and the molar ratio of nitrogen in the amino groups to carboxy in the organic carboxy acid being within the range of 4:1 to 1:2, said quantity being sufiicient to inhibit corrosion in said steam condensate system.

2. A method of inhibiting corrosion in return steam condensate lines which comprises introducing into the return steam condensate system a quantity of a composition resulting from heating an organic carboxy acid containing 8 to 36 carbon atoms and a polyalkylene polyamine containing at least two amino groups from the group consisting of primary and secondary amino groups at a temperature in the range of 115 C. to 300 C. and the elimination of an aqueous distillate, said organic carboxy acid being from the group consisting of acylic detergent forming acids and carbocyclic natural resin acids, the proportions of said carboxy acid being sulficient to acylate at least two mols of nitrogen in said polyalkylene polyamine and the molar ratio of nitrogen in the amino groups to carboxy in the organic carboxy acid being within the range of 4:1 to 1:2, said quantity being sufficient to inhibit corrosion in said steam condensate system.

3. A method of inhibiting corrosion in return steam condensate lines which comprises introducing into the return steam condensate system a quantity of a composition resulting from heating an unsaturated organic mono carboxy acid containing at least 8 carbon atoms and an aliphatic polyamine containing at least two amino groups from the group consisting of primary and secondary amino groups at a temperature in the range of C.

to 300 C. and'the elimination of anaqueousdistillate, the proportions of said carboxy acid. bein'g suificient to acylate at least one mol of nitrogen in said polyamine and themolar ratio offnitrogen in the amino groupsr=to carboxy. in the organic carboxy acid being within the range of 4:1 to 1:2, said quantity being sufiicient to inhibit corrosion in said steam condensate system.

4. A method of inhibiting corrosion in return steam condensate lines which comprises introducingsinto. the returnsteam condensate system a quantity of-a :composition resulting from heating a mixture of unsaturated organic monocarboxy acids and an aliphatiepolyamine containing at least two-amino groups from'the group consisting of'primary andsecondary-am'ino :groups at atemperature of at least 115 C. and-the elimination' of an aqueous distillate, at least one of said carboxy acids being an acid containing at least eight-carbon atoms in an acyclic hydrocarbon structure andanother being a carbocyclic natural resin acid, the amount of the smaller acid component being at least 15% by weight of the total amount of said acids, the proportions of said carboxy' acids beingsufi'icient to acylate at least one mol of nitrogen in saidpolyamine and the molar ratio of nitrogen =in'the amino groups to carboxy in the organic carboxy acid being within the range of 4:1 to 1:2, saidquantity being sufiicient to. inhibit corrosion in said steam condensate system,

.5. A method of inhibiting corrosion in return steam condensate lines which comprises introducing into the return steam condensate system a quantity-of a composition resulting from. heating, a mixture of unsaturated organic carboxy acids and a polyalkylene polyamine containing two terminal primary amino groupsat a temperature of at least 115 C. and the elimination of an aqueous distillate, said mixture of unsaturated monocarboxy organic acids containing at least two dissimilar unsaturated monocarboxy organic acids wherein at least one of said acids is a carbocyclic natural resin acid and another is an acyclic monocarboxy acid having at least 8 and not more than 36 carbon atoms in the chain, the'weight ratio of said acyclic monocarboxy acid to said carbocyclic monocarboxy acid being within the range of 1:2 to :1 and the lesser of said monocarboxy acids component always-being in excess of about by weight of the total monocarboxy acids, the proportions of said carboxy 1'2 acids being sufiicient to acylate at leastitwo mols of nitrogen .inxsaid polyalkylene polyamine, .said quantity being sufficient to inhibit corrosion in said steam. condensate system.

6. A method of inhibiting corrosion in return steam condensate lines which comprises introducing into the return steam condensate system a quantity of a-composition resulting from heating a mixture of tall oil, oleic acid and diethylenetriamine at a temperature of atleast C. and the elimination of an aqueous'distillate, the weight ratio of the acyclic carboxy acids to the carbocyclic carboxy'acids in said mixture being within the range of 1:2 to 5:1 and the lesser 'of said carboxy acids component always being in excess'of about 15% by weight of the total carboxy acids, and the proportions of said carboxy acids being sufficient to acylate at least'two' mols of nitrogen in said diethylenetriamine, said quantityjbeing sufiicient to inhibit'corrosionin said steam condensate system.

7. A- method of inhibting corrosion in return steam condensate lines which comprises introducing into the return steam condensate system a quantity of a composition resulting from heating a mixture of approximately 45.75% oleic acid, 45.75% tall oil and 8.5% diethylenctriamine and the elimination of-an aqueous distillate for approximately 24hours at a-temperature of about 115 C., said-quantity beingsuflicient to inhibit corrosion in said steam condensate system.

References Cited in the file of this patent UNITED STATES PATENTS 2,043,257 Missbach June 9, 1936 2,264,103 Tucker Nov. 25, 1941 2,328,551 Gunderson Sept. 7, 1943 2,396,471 Osterhof Mar. 21, 1946 2,426,338 Blair Aug. 26, 1947 2,521,311 Schwoegler et'al. Sept. 5, 1950 2,515,738 Smerech'n'iak et al July 18, 1950 2,550,682 Falkenburg et al May 1,- 1951 2,562,549 Hatch July 31, 1951 2,580,924 Jacoby Jan. 1, 1952 2,587,249 Ulmer Feb. 26, 1952 2,588,343 Bird et a1 Mar. 11, .1952 2,589,195 Monson Mar. 11, 1952 

1. A METHOD OF INHIBITING CORROSION IN RETURN STEAM CONDENSATE LINES WHICH COMPRISES INTRODUCING INTO THE RETURN STEAM CONDENSATE SYSTEM A QUANTITY OF A COMPOSITION RESULTING FROM HEATING AN ORGANIC CARBOXY ACID CONTAINING AT LEAST 8 CARBON ATOMS AND AN ALIPHATIC POLYAMINE CONTAINING AT LEAST TWO AMINO GROUPS FROM THE GROUP CONSISTING OF PRIMARY AND SECONDARY AMINO GROUPS, AT A TEMPERATURE OF AT LEAST 115* C. AND THE CLIMINATION OF AN AQUEOUS DISTILLATE, THE PROPORTIONS OF SAID CARBOXY ACID BEING SUFFICIENT TO ACYLATE AT LEAST ONE MOL OF NITROGEN IN SAID POLYAMINE AND THE MOLAR RATIO OF NITROGEN IN THE AMINO GROUPS TO CARBOXY IN THE ORGANIC CARBOXY ACID BEING WITHIN THE RANGE OF 4:1 TO 1:2. SAID QUANTITY BEING SUFFICIENT TO INHIBIT CORROSION IN SAID STEAM CONDENSATE SYSTEM. 